In vivo measurements of airway geometry and their mechanical properties are of fundamental use in pulmonary physiology and of clinical use in the assessment of lung airway disease, both for initial screening and for differential diagnosis. Radiographic bronchograms can be tediously analyzed to obtain dimensions of the airways. However, this proposal makes use of a rapid non-invasive technique, an acoustic impulse response from the airways, to obtain a measure of the input impedance over a frequency range that has been shown under the existing grant to contain information about airway geometry, including peripheral airways. An acoustic pressure pulse is applied as a barely noticeable input at the airway opening. The reflected pressure wave is recorded in time, and analysis of this wave and the incident wave results in an estimation of the impedance over the frequency range 100 to 10,000 Hz. These data are then analyzed using data inversion methods to obtain an estimation of the serial distribution of airway geometry. Results from the current grant indicate a close correlation between changes in airway cross-section determined radiographically and changes in the area-distance curves produced by this technique. The present proposal is thus to 1) continue applying the acoustic pulse response technique to measure changes in airway cross-section produced by pharmacological agents and mechanical intervention, 2) test this technique against direct measurements in order to assess its accuracy in estimating absolute cross-sectional area, and 3) to begin studies to determine mean values and variability in normal human subjects and the reproducibility of measurements.